Tungsten isomerization activity

J. C. Vartuli, J. G. Santiesteban, P. Traverso, N. Cardona-Martinez, C. Chang, and S. A. Stevenson, Characterization of the Acid Properties of Tungsten/Zirconia Catalysts Using Adsorption Microcalorimetry and n - Pentane Isomerization Activity, J. Catal. 187, 131-138 (1999). 

Excessive reduction, particularly after oxidation treatments favours hydrogenation probably due to the production of zero valent tungsten. The oxidized catalyst on the other hand lacks skeletal isomerization activity but shifts the double bond. This is a reaction characteristic of acidic catalysts. 

Fresh tungsten carbides catalyze hydrogenolysis of branched (neopentane, 3,3-dimethyl pentane, etc) and linear (hexane, heptane, etc) alkanes at high rates and with high selectivities to lower alkanes (47). The different C—C bonds are cleaved at about an equal rate, and there is negligible isomerization activity. The absence of isomerization products is not the result of rapid secondary hydrogenolysis of the products on the WC surface. Again, the rates and the product distribution are similar to those of Ru. 

The carbides and nitrides of the early transition metals have attracted considerable attention. Much of this can be attributed to the catalytic properties of these materials. Levy and Boudart1 were the first to note the Pt-like catalytic behavior of WC, which for many reactions is more catalytically active than metallic tungsten.2 Others have noted that the early transition metal carbides and nitrides, in general, are excellent catalysts for reactions characteristic of the more expensive noble metals.3,4 For example, WC has been found to catalyze the isomerization of neopentane to isopentane,1 a reaction that previously had been known to be catalyzed only by iridium and platinum.5... 

Some metal oxide catalysts are activated by thermal reduction with hydrogen or carbon monoxide. For example, the catalytic activity of molybdenum oxide and tungsten oxide for the metathesis reaction of olefins is very much enhanced by their slight reduction (1). The catalytic activity for butene isomerization and ethene oligomerization appears on niobium oxide by its... 

The active constituent of the catalyst is an oxide of tungsten prepared by partial reduction of WO - Unsupported WOj was found to have activity but better specific activity is obtained by depositing the oxide on a support. A number of grades of alumina and silica were tested. Gamma alumina was found to react with WOj at 400°C to a considerable extent to form aluminium tungstate. This was identified by XPS and tests on AljfWO ) showed it to be inactive as a catalyst for the isomerization reaction. 

The activity for skeletal isomerization exhibited by these tungsten catalysts is developed only under specific conditions of treatment and operation. The source of tungsten oxide and the method of support are not critical. The HT-alumina favoured in these tests had the advantage of good dispersion of WO and limited loss by reaction with the support to form aluminium tungstate. 

The specific metal-snpport interaction existing for CNTs or CNFs has been demonstrated in several stndies. A strong interaction between the H3PW12O40 heteropolyacid and the snrface gronps of MWCNTs was reported for the esterification of n-bntanol with acetic acid [371]. For olefin skeletal isomerization on WO3/MWCNT [344], it was shown that on CNTs, by contrast to oxide snpports such as alumina and zirconia, the formation of metallic tungsten is inhibited, thus pointing to the absence of an observable deactivation phenomenon. For dibenzotiophene HDS, TPR data have shown that the active species on Co and... 

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